MEMS are miniaturized devices (i.e., micrometer dimensions) that include actuators, sensors, and other electro-mechanical structures. MEMS are typically fabricated by bulk-etching a silicon substrate or depositing layers of polysilicon, oxides, metals, and the like on top of a silicon substrate. Typical MEMS actuation mechanisms include electrostatic, magnetic, and thermal. A MEMS thermal actuator is a micromechanical device that typically generates motion by thermal expansion amplification. A small amount of thermal expansion of one part of the device translates to a large amount of deflection of the overall device. MEMS thermal actuators are typically fabricated out of doped single crystal silicon or polysilicon as a complex compliant member.
Thermal actuators are widely used in MEMS devices that require high displacement and/or high force, and are most often implemented in a v-beam, u-beam, or bimorph configuration. In all of these configurations, Joule heating from an applied electrical current causes an actuator material (typically silicon) to expand providing a net displacement of the actuator. It is often desired to operate the actuator at a maximum displacement point. However, if the applied electrical current is increased much beyond a maximum deflection point, the actuator material can melt.
MEMS actuator displacement is conventionally controlled using a switch implementation. When the actuator moves to the desired position, an electronic loop is closed thus providing feedback to inform power supply electronics that the power being provided to the actuator is sufficient. However, for every feedback signal needed to control displacement, there are a set of pads required to feed the signal into the MEMS package and respond with the feedback signal. With multiple actuators on one chip, this could double pin counts in a package, thus increasing real estate. Also, it is not efficient to have to tune each power supply for the actuators.